French patent specification FR 2 641 018 relates to an assembly device for elevator shafts. It is attached to the door threshold and has two parallel bars that rest against the opposite wall. In addition, a supporting ladder element is provided as the mode of access to a horizontal work platform. The bars are configured as telescopic rods with locking pins and they enclose an angle of 25° relative to the horizontal. This assembly device is very complex and configured with numerous parts. A rapid and simple assembly is not possible.
Moreover, a work stage is known that has the following features (DE 199 28 574 C2). The work stage comprises a device for receiving and/or positioning a work platform. The device serves to position the work platform and is equipped with a holder or a support part on which the work platform is adjustably arranged and that serves as a bracing part. For this purpose, the holder has an arrangement by means of which the work platform can be supported on one side against a counter-support or against a wall. Moreover, on an opposing side, the work platform has a second arrangement that can likewise be supported against a counter-support or a wall by means of the support part. Facing the opposing side, the holder has a safety mechanism for the work platform that consists of a holding means and of a beam as a supporting device and that has a second support part that can be laid against the wall. The holding means is configured as a tie rod whose one end is connected to the work platform and whose other end is movably connected to the beam. In order for the work platform to be supported, it has to have at least two side walls that are opposite from each other and provided in a shaft section.
German patent specification DE 803 075 C as well as world patent application WO 00/70169 A both describe a work stage with a vertical strut that is rigid with respect to the door opening, whereby a crossbeam for receiving a work platform is bearing-mounted so as to swivel on said vertical strut. The crossbeam is affixed on its side opposite to the vertical strut by means of a tie rod that is attached to the vertical strut above the crossbeam. The tie rod can be articulated so that the work platform can be folded open and closed.